It is generally said of solid state ballasts in high frequency lighting that they provide the advantages of reduction in weight and size, improvement in the luminous efficiency of radiation, compatability both to 60 Hz and 50 Hz, and removal of flickers and ballast noises and the likes. With regard to ballasts for domestic use, as distinguished from those for business use (office, workshop, etc), however, it is considered that such advantages are still insufficient; the essential advantage of domestic high frequency lighting resides rather in that the use of a plurality of miniature components is enabled by RF lighting (for example, 20 KHz), which increases the degree of freedom in circuit design. The inherent features of a solid state ballast for domestic use in high frequency lighting can be considered, plainly, as the introduction of the simplicity and convenience of an incandescent lamp as much as possible while retaining the merits of a fluorescent lamp. Basic functions necessary for realizing the above features include:
(i) provision of versatile and flexible functions as a ballast circuit for fluorescent lamp; PA1 (ii) elimination of waveform interference, in particular, radio wave interference accompanying high frequency operation, as well as retention of lamp compatibility with regard to the use of a pre-heat start type fluorescent lamp; and PA1 (iii) fail-safe and fool-proof functions necessary for keeping high reliability and the like. PA1 (a) light control for a fluorescent lamp by way of an entire 2-line system (generally a 3-line system), a common light control for a plurality of fluorescent lamp appliances and thus an applicability to indirect lighting or the like, pre-set light control and a stepwise light control for pendant appliances by the use of a simple exclusive switch; PA1 (b) rapid starting and practically instant starting, if required, by reducing the required starting time; PA1 (c) operation for a multiplicity of lamps, which is an essential function in view of cost and simplicity for lighting appliances, both for a plurality of appliances of a same kind and for a plurality of appliances of different kinds.
Among the above, the functions (iii) are additional circuit function; and these have only to be noted to attain them in a simple construction. On the contrary, special skill is required to satisfy both of the functions (i) and (ii) in combination, which is the object of the present invention.